Power factor correction circuit

Abstract

A power factor correction circuit includes a series circuit in which a reactor L and a control switch Q 1 are connected in series to both ends of a rectifier circuit 2 that rectifies input voltage of an AC power supply, a series circuit in which a synchronous rectification switch Q 2 and an output capacitor C 1 are connected to two main terminals of the control switch, and a control circuit 10 that alternately turns on and off the control switch and the synchronous rectification switch so that output voltage of the output capacitor becomes a first predetermined value and controls ON time of the control switch so that a peak value of current flowing through the control switch is proportional to input voltage. The control circuit turns on and off the control switch and the synchronous rectification switch so as to adjust a reverse excitation amount for reverse excitation of the reactor by causing current flowing through the reactor to reversely flow from the output voltage side to the input voltage side, and the reverse excitation amount is adjusted to a second predetermined value regardless of input voltage Vi.

The invention claimed is: 
     
         1 . A power factor correction circuit comprising:
 a reactor including one end connected to one end of an AC power supply and another end connected to a first main terminal of a control switch;   a first series circuit in which a synchronous rectification switch and an output capacitor are connected in series to the first main terminal and a second main terminal of the control switch;   a second series circuit in which a first polarity changeover switch and a second polarity changeover switch are connected in series to both ends of a series circuit of the control switch and the synchronous rectification switch; and   a control circuit that alternately turns on and off the control switch and the synchronous rectification switch so that output voltage of the output capacitor becomes a first predetermined value to control ON time of the control switch so that a peak value of current flowing through the control switch is proportional to input voltage of the AC power supply, and switches the control switch and the synchronous rectification switch according to polarity of input voltage of the AC power supply and switches processing of turning on one of the first polarity changeover switch and the second polarity changeover switch and turning off another one of the first polarity changeover switch and the second polarity changeover switch,   wherein   the control circuit turns on and off the control switch and the synchronous rectification switch so as to adjust a reverse excitation amount of reverse excitation of the reactor by causing current flowing through the reactor to flow backward from an output voltage side to an input voltage side, and   the reverse excitation amount is adjusted to a second predetermined value regardless of the input voltage.   
     
     
         2 . The power factor correction circuit according to  claim 1 , wherein the reverse excitation amount is determined using an inductance value L of the reactor, parasitic capacity C of the control switch, and the output voltage Vo. 
     
     
         3 . The power factor correction circuit according to  claim 2 , wherein the reverse excitation amount is determined by a first mathematical formula (√{square root over ( )}(C/L)×Vo×α including a coefficient based on the inductance value L of the reactor and the parasitic capacity C of the control switch, the output voltage Vo, and a first term α that is a real number of one or more. 
     
     
         4 . The power factor correction circuit according to  claim 2 , wherein the reverse excitation amount is determined by a second mathematical formula (√{square root over ( )}(C/L)×(Vo×α+β) including a coefficient based on the inductance value L of the reactor and the parasitic capacity C of the control switch, the output voltage Vo, and a first term α and a second term β that are real numbers of one or more, the second term β being a harmonic having a frequency n times an input frequency (n is an integer of three or more). 
     
     
         5 . The power factor correction circuit according to  claim 4 , further comprising:
 a reverse excitation current detection unit that detects reverse excitation current flowing when the reactor is reversely excited; and   a zero voltage switching determination unit that determines that zero voltage switching of the control switch is possible when a value of reverse excitation current detected by the reverse excitation current detection unit is equal to or more than a value determined by the second mathematical formula.   
     
     
         6 . The power factor correction circuit according to  claim 3 , wherein the control circuit includes a first calculator that calculates first ON time of the control switch based on input current flowing through the reactor, the input voltage, and a reactance value of the reactor, and adds, to the first ON time, second ON time determined by a reactance value of the reactor, a parasitic capacity value of the control switch, the input voltage, the output voltage Vo, and the first term α to obtain ON time of the control switch. 
     
     
         7 . The power factor correction circuit according to  claim 4 , wherein the control circuit includes a first calculator that calculates first ON time of the control switch based on input current flowing through the reactor, the input voltage, and a reactance value of the reactor, and adds, to the first ON time, second ON time determined by a reactance value of the reactor, a parasitic capacity value of the control switch, the input voltage, the output voltage Vo, the first term α, and the second term β to obtain ON time of the control switch, the second term β being a harmonic having a frequency n times an input frequency (n is an integer of three or more). 
     
     
         8 . A power factor correction circuit comprising:
 a rectifier circuit that rectifies input voltage of an AC power supply;   a first series circuit in which a reactor and a control switch are connected in series to both ends of the rectifier circuit;   a second series circuit in which a synchronous rectification switch and an output capacitor are connected in series to two main terminals of the control switch; and   a control circuit that alternately turns on and off the control switch and the synchronous rectification switch such that output voltage of the output capacitor becomes a first predetermined value, and controls ON time of the control switch such that a peak value of current flowing through the control switch is proportional to the input voltage,   wherein   the control circuit turns on and off the control switch and the synchronous rectification switch so as to adjust a reverse excitation amount that reversely excites the reactor by causing current flowing through the reactor to flow backward from an output voltage side to an input voltage side, and   the reverse excitation amount is adjusted to a second predetermined value regardless of the input voltage.   
     
     
         9 . The power factor correction circuit according to  claim 8 , wherein the reverse excitation amount is determined using an inductance value L of the reactor, parasitic capacity C of the control switch, and the output voltage Vo. 
     
     
         10 . The power factor correction circuit according to  claim 9 , wherein the reverse excitation amount is determined by a first mathematical formula (√{square root over ( )}(C/L)×Vo×α including a coefficient based on the inductance value L of the reactor and the parasitic capacity C of the control switch, the output voltage Vo, and a first term α that is a real number of one or more. 
     
     
         11 . The power factor correction circuit according to  claim 9 , wherein the reverse excitation amount is determined by a second mathematical formula (√{square root over ( )}(C/L)×(Vo×α+β) including a coefficient based on the inductance value L of the reactor and the parasitic capacity C of the control switch, the output voltage Vo, and a first term α and a second term β that are real numbers of one or more, the second term β being a harmonic having a frequency n times an input frequency (n is an integer of three or more). 
     
     
         12 . The power factor correction circuit according to  claim 11 , further comprising:
 a reverse excitation current detection unit that detects reverse excitation current flowing when the reactor is reversely excited; and   a zero voltage switching determination unit that determines that zero voltage switching of the control switch is possible when a value of reverse excitation current detected by the reverse excitation current detection unit is equal to or more than a value determined by the second mathematical formula.   
     
     
         13 . The power factor correction circuit according to  claim 10 , wherein the control circuit includes a first calculator that calculates first ON time of the control switch based on input current flowing through the reactor, the input voltage, and a reactance value of the reactor, and adds, to the first ON time, second ON time determined by a reactance value of the reactor, a parasitic capacity value of the control switch, the input voltage, the output voltage Vo, and the first term α to obtain ON time of the control switch. 
     
     
         14 . The power factor correction circuit according to  claim 11 , wherein the control circuit includes a first calculator that calculates first ON time of the control switch based on input current flowing through the reactor, the input voltage, and a reactance value of the reactor, and adds, to the first ON time, second ON time determined by a reactance value of the reactor, a parasitic capacity value of the control switch, the input voltage, the output voltage Vo, the first term α, and the second term β to obtain ON time of the control switch, the second term β being a harmonic having a frequency n times an input frequency (n is an integer of three or more).